Observed bill reduction after attic insulation retrofit
I’m going to have my attic insulated up to r-60. I was wondering what kinds of reductions project have seen in their heating/cooling bills after performing a similar retrofit.
Let me add some more details. I understand that air sealing is more important than insulation.
My question was more for people that have done a retrofit, have air sealed and also added insulation. I have looked around, and the best I can do is find sites that claim up to “40% odd amount off your bills!” but no actual numbers.
I do understand that everyone’s experience is different, but still, what was your experience? Did you bills go down by a small amount? Or a large amount?
And, while I’m at it, did you add anything else? Heat pump water heater? Mini-split?
While everyone’s experience is different, I would think that being able to share your experience retrofitting and seeing the difference in this particular way could help myself and others when figuring out if they should go whole hog, or something more modest.
Thanks in advance!
Joel
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
The reduction is dependent on what you are starting with.
Before adding anymore insulation, come up with a plan for air sealing the ceiling below. Air leakage is likely a bigger heat loss component than the insulation you are considering adding.
It's been about 9 years, but as I recall, installation of our heat pump water heater dropped electricity consumption by around 150 kWh/month. With a utility rebate and Federal tax credit, payback was just a few years.
Be sure to investigate and include any incentives and rebates in your calculations. The local utility is currently offering a $500 rebate on HPWH.
We also added insulation and air sealing in the attic but I don't have figures that I can point to because we also used a woodburning fireplace insert. Between the two, heating oil consumption was cut in half, mostly due to the wood stove.
In 2006, our electrical consumption was 10,781 kWh. In 2014, it was 5,058 kWh. That reduction was the result of incremental improvements in lighting, better appliances, etc. Consumption has increased somewhat with the addition of an EV.
Joel,
I have done such a project, went from R-22 to R-50 on the cathedral portion of the ceilings and R-30 to R-50 on the flat ceiling. Air sealing was comprehensive in both areas and I am seeing around a 24% reduction in natural gas usage compared to before the retrofit. We did a blower door test before any work was started and will do one in the next couple of months to see what improvement was made in reducing infiltration. I would say air sealing is at least equal in importance to adding insulation in lowering energy usage for this type of project. Will the energy savings pay for the retrofit? It will take a number of years but the added benefit of eliminating ice dams on this house has to be part of the equation.
I had a leaky cathedral ceiling over about 500 square feet or so. “Leaky” means cut and NOT cobbled (pieces of 2” XPS loosely slid between rafters) rigid foam insulation, tongue and groove ceiling with no drywall, and some “vents” in the roof so indoor air could leak outside.
I put in R38 of closed cell spray foam and put a lot of effort into air sealing the perimeter walls. The following winter season, we had lower average outdoor temperatures but were keeping the indoor temperature more consistent throughout the day due to a new baby. We had lower gas bills despite the lower outdoor temperatures and more heating time during the day.
It’s worth the effort to do the work, but how much benefit you see depends entirely on what you’re starting with.
Bill